1. Field of the Invention
The invention pertains to a chip module with a contact layer made of electrically conductive material, a multiplicity of contact elements on the front side with contact areas, and a semiconductor chip disposed above the contact layer. The semiconductor chip has chip terminals, which are arranged on a main area of the semiconductor chip and are electrically connected via bonding wires to the back side of the contact element assigned to the chip terminal. The chip module is to be installed in particular into a chip card.
Chip cards have manifold application purposes. They are generally made in check card format and they have become extremely varied on account of thei high functional flexibility and, with the increasing computing power and storage capacity of the available integrated circuits, their use continues to increase. Apart from the currently typical field of application of such chip cards in the form of cards for medical insurance policyholders, flexitime acquisition cards and phonecards, in future there will be in particular applications in electronic payment systems, for computerized access control, for protected data memories and the like. Various possibilities exist currently for producing chip cards. In most methods, the actual semiconductor chip is initially mounted onto a chip card module, which also comprises the usually gold-plated card contacts. The chip card modules are usually produced on a continuous tape or continuous substrate, the individual chip card modules are subsequently punched out and introduced into the chip card. In this method, no direct attachment of the chip in the card takes place. This has the advantage that the flexural forces and shear forces which may occur under mechanical loading of the chip card are largely kept away from the chip. In the production of chip card modules, most often used at present is the so-called wire-bonding method, upon which the module according to the invention is also based. Such wire bonding is disclosed, for example, in French disclosure FR 2 684 236 A1, in British specification GB 2 149 209 A, and in German disclosures DE 42 32 625 A1 and DE 38 09 005 A1. There, the chip terminals of the semiconductor chip bearing the actual electronic circuit are connected by thin bonding wires to the individual contact elements of the contact layer. For protection against environmental influences, the semiconductor chip and the bonding wires are covered with a casting composition. The advantage of that production process is that it is based largely on the processes which are customary in the semiconductor industry for packing chips in standard packages. As a result the process is less expensive. The main disadvantage of the method is that both the overall height and the length and width of the module turn out to be much greater than, for example, in the case of the so-called TAB module, in which the terminal areas (pads) of the semiconductor chip are provided with electrodeposited metallic humps, which serve for the direct attachment of the electrically conductive contact areas by solder connection. There it is consequently not necessary to cover the bonding wires.
For the incorporation of the chip module in the chip card, currently three different methods have become established, the laminating method, insertion into milled cavities, and mounting in ready injection-molded cards. In all the methods of incorporation, the card producer faces the disadvantage of having to insert into the card chip card modules of different overall sizes, which result from the different chip area of the semiconductor chip used. The diversity of modules resulting from different chip areas of, typically, about 1 mm.sup.2 to 20 mm.sup.2, also causes the module producer to incur increased material costs owing to reduced delivery volume per module variant and increased expenditure on logistics. Owing to the different module types, the card producer is faced with different dimensions of the card cavities for the incorporation of the module and consequently with increased tool costs and process costs.